Liquid level control apparatus



Oct. 27, 1953 B. L. covlm' Erm.

LIQUID LEVEL CONTROL APPRTIJS Filed July 29, 1950 wma mm3... zwar-.Ow

INVENTORS: BENJAMIN L. COVERT. HAROLD E. DAHLQUIST. cm

BYZ l z, t

ATTORNEYS;

Patented Oct. 27, 1953 LIQUID LEVEL CONTROL APPARATUS Benjamin L. Covert and Harold E. Dahlquist,

Chicago, Ill., assignors to lUniversal lOil 'Prodzucts Company, Chicago, -Il1.,.a corporation of Delaware Application July 29, 1950,'Serial N 051765568 (Cl. S17-132) Vi) Claims.

This invention relates to an improved type of electronic liquid level control apparatus, yand more particularly toa relatively Asimple electronic type 'of controller which may be utilized to maintain substantially accurate liquid levels, within small liquid receiving chambers.

Many of the present -forms of liquid level ycontrollers are of a type which are not suitable Afor use with very 4small liquid receiving chambers, such as -may be used 'in laboratory apparatus or pilot plants, or they are not adapted for use with extremely high pressure'equipment because of yinadequate packing glands or sealing means. Still other types of liquid level 'controllers are adapted to operate overa relatively wide range of level variations and are not sensitive to small changes ,in liquid' level.

It is, therefore, a principal vobject ofthe'present invention to Vprovide a sensitive type Yof liquid level controller which is Yadapted to operate quickly and accurately `within small 'liquid receiving chambers without too much hold-up cf the liquid material.

It is a 'further object ofthe present invention to provide a control instrument 'which uis Vof :the electronic type adapted Ato operate in connection with small liquid liows at high pressure, vand utilizing a resistance coil sensing element connecting with a balancing resistor and a ltransformer in a resistance phase changing circuit, whereby resulting voltage changes operate a relay and pilot Valve.

"lt is a still further object of the improved `instrument to provide a control apparatus which may be utilized `in connection with either large or small liquid receiving chambers and may be constructed and operated in a relatively inexpensive manner.

Briefly, the improved electronic liquid `level control apparatus of this Yinvention comprises in combination, an electrical resistance sensing coil adapted to be positioned within areceiving chamber at a desiredliquid level therein, wirinjg connecting the sensing coil with one end of a secondary coil of ya transformer and one end of Aa balancing resistor, the latter connecting to the other end of the secondary .coil rand the secondary coil having a grounded center tap ywhereby changes inresistance from thesensing coil .eiect changesin the voltage output from the secondary coil, wiring connecting one end of the sensing coil and the accompanying end of the balancing resistor to a control grid of a 'iirst stage amplifying .tube in an electronic amplifying and rectif ying circuit, means connecting Va rectified voltage ill from the latter `circuit -to the vcontrol grid of a power tube, a direct'current power supply to the anodesol each-of t-he tubesof the circuits, an electrical relay connected inthe direct current power suply line to the anode of the power tube, whereby fthe relay may operate'a pilot valve connecting therewith, the pilot Valve in turn connecting with and operating an 'automatic liquid iiow vcontrol -valve in a fluid conduit communieating with `-the liquid receiving chamber. 'The relay -and pilot valve are/connected in a manner to be responsive to direct cur-rentiiow to `the anode ofthe -poWer-tube,and the direct current flowin turn -is regulated-and controlled by a resulting'voltage `applied to the control grid of the power tube `from the y'rectified phase voutput of the secondary coil of the transformer which is initiated vby the sensing coil.

Preferably the sensing element, Ior resistance coil, conecting with the secondary transformer, is mounted'withinthe liquidreceiving chamber so that it is just 'abovetheliquid level desired within the chamber and out vof contact with the liquid for a balancing of the'electronicfcircuit. In other words, Vthe Acircuit is 'arranged so that when -the sensing element is out Vo f'liquid there is a phase balance, with 'no 1voltage flowing from the Voutput of the secondary coil ofthe transformer. Thus, when the 'liquid level changes and reaches the sensing element there is a resistance change which Ain turn provides a phase output'from the transformer coil. AThe voltage of `this phase output .is then .recti-iied and 4supplied to the control grid of the power tube. .A current owfrom the control `grid of the power'tube then operates to cut olif-current flow to the anode or plate thereof and 'in turn effect a release of van armature of a relay which is placed adjacent a pilot control valve. Preferably an air pilot valve is utilized which is sensitive to any changes in the pressure, or lback pressure, exerted against a pilot air stream, so that thepilot valve ymay operate an automatic air or Ymotor controlled 4valve within a jfiuidconduitto theiliquid Vreceiving chamber, to in turn control fluid :How to, or away from, the Chamber and maintain a desiredliquid level.

The construction andoperation of the-improved electronic liquid level control apparatus lwill be moreapparent upon reference'to the accompanying drawing and thefollowing descriptionthere of, while in addition, 'further advantages of the improved 'apparatus will lbe noted in lconnection therewith.

Referring nowto the drawing, there is indicated diagrammatically a sensing coil l within a protecting sleeve or well 2 and mounted at a de sired liquid level 3 within a liquid receiving chamber 4. The resistance coil I may be of nickle, or other suitable wire, and wound in the form of a heating coil, while the sleeve or well 2 may be of tubular form with a closed lower end so that it may protect the resistance coil from direct contact with the liquid medium in the chamber. Stainless steel or other alloy may be desirable where corrosive materials are handled in the liquid receiving chamber 4.

The resistance coil I connects by means of wire to a balancing resistor II by wire 6 to the end of the secondary coil of a transformer "l, the latter being supplied with a suitable substantially constant voltage alternating current. rllhe center tap of the secondary coil of transformer 'I is grounded by a suitable Wire 8, so that opposing phase circuits are provided from ground to line il and line 3 which connects with the grid of a first stage amplifying tube il), of an amplifying and rectifying circuit.

In a preferred arrangement, the sensing coil I is positioned such that it is just above a desired liquid level within the chamber i and is joined with the transformer 'I in a resistance phase changing circuit so that when the ele ment is out of the liquid there is a phase balance within the circuit and no voltage ilows from the output of the secondary coil of the transformer. The balancing resistance II in the control circuit maintains the output balance so that no voltage flows under this condition. However, when a liquid level 3 within the chamber' 4 reaches the element, there is a resistance change due to a change in temperature of the sensing coil so that there is a change in phase output from the transformer l. The resulting voltage from the phase output is carried through a two-stage amplication circuit and a rectifying circuit to thus provide a higher direct current voltage at a power control tube.

The amplifying and rectifying circuits, having the amplifying tubes It and I3 and a rectifying tube I4, receive suitable anode power by way of a direct current source connecting to lines l5 and I6. Lines II and I3, and the respective plate resistances 2l and 22, connect with the lines I3 and 20, which in turn connect with the respective anodes of amplifying tubes I0 and I3. The ground lines i3 and 23 connect through suitable bypass condensers 24 and bias resistances 25 to the cathodes of each of the amplifying tubes I0 and I3. Line I3 connects with a suitable coupling condenser 23 and the latter connects with a suitable adjustable gain control resistance 21 which is placed from condenser 26 to ground line 23. rllhe adjustable tap of the gain control 2'I connects directly with the grid oi' amplifying tube I3, such that the amplifying circuit may be properly controlled. The phase output from the amplifying circuit carries by way of line 2li and the coupling condenser 23 through line 29to the anodes of the rectifying tube I4. A load re-u sistance 3e also connects between ground line 23 and the anode line 29.

A resulting rectified direct current voltage from the cathode of rectifying tube I4 passes by way of line 3i to the control grid 32 of a power control tube 33. A filter condenser 34 and a load resistance 35 connect between line 23 and line 3l, the latter connecting with the control grid of the power tube 33, while the ground line 23 connects directly with the cathode 36 of the power tube. Direct current anode power for the tube is carried by way of lines I6 and 31, relay coil 33, and line 33 directly to the anode of the power tube. The screen grid 4I) also receives power by way of line 39 and resistance 4I.

4The relay coil 38 is, in the present electronic system, Wound around a suitable iron core 41 which is adjacent a movable armature 48 at the end of a relay box 49. Thus, in operation, when there is no voltage ilow to the control grid 32 of the power tube 33, then direct current flows through the anode circuit of the power tube, passing by way of line 3l and coil 38 and line directly to the anode of the tube. With current flow through the relay coil 38, the core 41 is energized and the movable armature 48 is pulled away from the air nozzle 42 actuating an air pilot valve 43 which tends to open, or alternatively, close a diaphragm or motor control valve ill by means of air line 45. The control valve 4f?. in turn is placed within a fluid conduit lit which communicates with the liquid receiving chamber' 4 so that fluid flow to, or from, the chamber may be controlled to maintain the given desired liquid level within the retaining chamf ber.

When the sensing coil I of the liquid level controlling apparatus changes resistance so as to effect a phase change, the output voltage is amplified and rectified so that a resulting D. C. voltage passes tc the control grid 32 of power tube With this voltage flow to the control grid, the current liow through the power tube is cut off and the result is that 'there is no voltage flow through the relay coil 3c and the air pilot valve 43 is actuated by the armature 43 stopping the new of air from the nozzle 42. As previously noted, the amplifying and rectifying circuit oi the apparatus is preferably balanced when the liquid level 3 is out of contact with the sensing coil i and the enclosing sleeve or well 2, with opposing phases of the secondary coil balancing one another and a current flow effected only when there is a change in resistance at the sensing coil I and a resulting voltage phase output from liquid coming in contact with a lower end of the well 2. Thus, when there is no ow to the control grid 32 of the power tube 33, anode power is continuously supplied thereto and air pilot valve 33 is maintained in an open position by means of the relay armature 43 and nozzle cl2. The air pilot valve being in turn connected with control valve fifi, such that air is passed by way of line or tube 43 to the diaphragm of the 'control valve 43 and fluid ilow effected either to or from the chamber d. Where there is fluid flow through the valve 4d and conduit 43 to the liquid receiving chamber i for an energized relay and no current to the control grid then a resulting liquid level contact with the sensing coil I effects a voltage new to control grid 32 and a cutting off of the current flow through the anode circuit of the power tube 33 which in turn effect a cutting off of the fluid supply through the control valve 44 and to the chamber Il.

The control apparatus may of course be connected or hooked-up such that the air pilot valve 43 opens the control valve 44 when there is a voltage output from a sensing coil and a release of the relay coil 38, to allow uid flow away from the chamber 4. 1n 'this alternative arrangement, a voltage output from the sensing coil may operate control grid 32 to cut off the voltage to the anode of the power tube and current flow through relay 33 such that the air pilot valve may open the control valve 44 and allow flow through the conduit 46 away from liquid receiving chamber' 4 to in turn effect a lowering of the liquid level 3. Fluid in this instance being supplied through a fluid inlet conduit connecting with chamber 4 and not shown in the present drawing.

This improved electronic control system is of particular advantage in that it is not subject to pressure changes within the liquid receiving chamber 4 and it is unnecessary to have any type of packing glands or sealing means around mee chanically moving parts. An electrical resistance coil of the type used in electronic circuit of this apparatus is also particularly sensitive to small changes in temperature and thus acts to issue a voltage output or phase change from the secondary coil 'of transformer 1 immediately upon being contacted with liquid level 3, to in turn provide a sensitive type of level controlling apparatus which does not permit a wide range in variation of the liquid level 3. This present liquid level controlling apparatus has an advantage over the float type 'of level controls, where it is necessary to have a relatively large chamber to accommodate a movable float.

The resistance coil I and protecting sleeve or well 2 may be readily inserted in small vessels or chambers such as may be used in laboratory or pilot plants as well as in connection with large commercial size plants or installations, and is of course immediately sensitive to any liquid co-ntact therewith. Apparatus of this type may be used advantageously with small iiuid flows of the order of 100 cubic centimeters per hour or less, with either atmospheric or high superatmospheric pressures being utilized within the liquid receiving chamber itself.

We claim as our invention:

1. An electronic liquid level control apparatus comprising a sensing coil, wiring connecting one end of said sensing coil with a balancing resistor. and wiring connecting the other end of said sensing coil and of said resistor with each end of a secondary coil of a transformer, said secondary coil having a grounded center tap whereby changes in resistance from said sensing coil change the Voltage output from said transformer secondary coil, wiring connecting one end of said sensing coil and the accompanying end of said balancing resistor to the control grid of a first stage amplifying tube in an electronic amplifying and rectifying circuit, means connecting a rectified voltage from said circuit to the control grid of a power tube, a direct current power supply to the anodes of each of the tubes of said circuits, and an electro-magnetically controlled delecting member connected in the direct current power supply line to the anode of the power tube, and with said deflecting member moving substantially linearly responsive to the current in the anode circuit of said power tube.

2. An electronic liquid level control apparatus comprising a resistance coil sensing element having a protecting sleeve precluding the latter coming into direct contact with a liquid medium, wiring connecting said sensing element with one end of a secondary coil of a transformer and one end of balancing resistonsaidresistor connecting to the other end of said secondary coil, and said transformer receiving a constant voltage alteranting current and having a grounded center tap whereby changes in temperature and resistance from said sensing element change the voltage output from said secondary coil of said transformer, wiring connecting one end of said sensing element and the accompanying end of said balancing resistor to the grid of a first stage amplifying tube in an electronic amplication circuit, additional wiring and suitable isolating condensers and resistances therein connecting the ampliiication circuit to a rectifying tube in a recticaton circuit, the resulting rectined voltage output from said rectifying tube connecting to the control grid of a power tube, a direct current power supply to the anodes of the tubes of said amplincation and rectication circuits, and a direct current power supply line to the anode of said power tube with an an electro-magnetically controlled deflecting member connected in series therein and moving in a substantially linear manner responsive to current flow to the anode of said power tube, whereby iiow control means may be regulated directly responsive to said resistance coil sensing elements.

3. The electronic liquid level control apparatus of claim 2 further characterized in that said secondary coil of the transformer and said circuits are balanced Such that there is no voltage output from said transformer when said sensing element is out of contact with liquid, whereby direct current is supplied to the anode of said power tube through said relay, and a resulting change in resistance from said sensing element supplies the voltage to the controlling grid of said power tube and cuts off the current ow to the anode of said power tube.

BENJAMIN L. COVERT. HAROLD E. DAHLQUIST.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,150,440 Hargreaves c Mar. 14, 1939 2,228,163 Cohen Jan. 7, 1941 2,310,298 Kuhl Feb. 9, 1943 2,323,128 Hare June 29, 1943 2,456,233 Wolf Dec. 14, 1948 2,457,165 McNamee Dec. 28, 1948 2,550,430 Schwarz Apr. 24, 1951 

